Process for the manufacturing of an article of plastic material

ABSTRACT

Article made of thermoplastic material, which article is rigid and at least partly heat insulating. The article includes a laminate in at least parts of the article. The laminate includes a first and a second layer of solid thermoplastic material (A) and an intermediate layer of expanded thermoplastic material (B) with an average density of 50-800 kg/m 3 . The thermoplastic materials (A) and (B) are the same or compatible materials. The article is manufactured according to a process comprising the steps a) forming of a solid outer layer, b) manufacturing of an intermediate expanded layer and c) the appendage of functional parts such as reinforcing profiles, guiding profiles, stacking profiles, hinge parts, pockets, label holders, profiles or holes for automatic handling, locking devices or the like.

The present invention relates to an article made of plastic material,which article at least partly includes a laminate which comprises alayer of expanded plastic material, and the process for manufacturingsuch an article.

Articles made of plastic material with a heat insulating ability havebeen commonly known for a long time. One example of such an article arecontainers made of expanded thermoplastic styrene, so-called styro-foamcontainers. These containers are excellent as heat insulators but have avery poor mechanical stability which will give them the characteristicsof a disposable package. The surface of these containers is furthermoreporous, which will make them rather difficult to keep clean. They aretherefore less suited for use in the food supply industry.

Another type of articles made of plastic material is the rotationmoulded plastic pallet. Initially a skin of solid thermoplastic materialsuch as polyethylene or polypropylene is manufactured. The skin is aftercooling filled with an expanded thermosetting polymer, most oftenpolyurethane. Surf boards are also manufactured by this procedure. Thereason for the use of expanded polymer is not the insulating effect inthese cases, but the stabilising effect that will be obtained.

Yet another type of articles made of plastic material, are manufacturedby blow moulding. These can be made twin-walled with an intermediatehollow space. Compost receptacles can be mentioned as an example of sucharticles. The hollow space can be filled with an expanded polymer if anincreased heat insulating ability is desired. Normally a thermosettingmaterial of polyurethane will be used.

One disadvantage with these processes is that the articles obtained willbe impossible to recycle by material recovery since the materials usedare not compatible. It is also difficult to provide the articles withwell defined functional parts such as reinforcing profiles, guidingprofiles, stacking profiles, hinge parts, pockets, label holders,profiles or holes for automatic handling, locking devices or the like,due to the coarse manufacturing tolerances allowed by these processes.It is therefore possible to use these processes for ordinary articlesonly since functions provided by functional parts as for example in acollapsible pallet container are impossible to manufacture.

It is desirable to achieve re-cyclable, heat insulating and rigidarticles made of plastic material, that additionally are manufacturedwith the same accurate tolerance and functionality that can be achievedby traditional injection moulding. It is possible to achieve the abovementioned desires according to the present invention, whereby arecyclable article made of plastic material, which article is providedwith an even and dense surface, an insulating and/or stabilising innerlayer and well defined functional parts, can be manufactured.Accordingly, the invention relates to an article made of plasticmaterial, preferably a transport and/or storage article such as apallet, a pallet collar, a pallet container, a receptacle, a container,a crate, a compost receptacle, a waste receptacle or the like. Thearticle is rigid and at least partly heat insulating and is manufacturedof a thermoplastic material selected from a group consisting ofpolyethylene, polypropylene, polybutene, polyvinylchloride,polyalkylene-terephthalate, polystyrene, acrylonitrile-butadiene-styreneco-polymer or the like. The article includes laminate parts in at leastparts of the article. The invention is characterised in that thelaminate parts comprise a first and a second outer layer of a solidthermoplastic material A and an intermediate layer of a expandedthermoplastic material B with an average density of 50-800 kg/m³.Together, the layers form a laminate. The thermoplastic materials A andB are the same or compatible materials, whereby a re-cyclable plasticarticle is obtained.

The article is preferably provided with functional parts such asreinforcing profiles, guiding profiles, stacking profiles, hinge parts,pockets, label holders, profiles or holes for automatic handling,locking devices or the like. The functional parts are applied on thearticle by welding, confounding, screwing, riveting, gluing or snap-injoining. The functional parts are manufactured from a thermoplasticmaterial included in the same group as the thermoplastic material A andB.

The first and the second layer, which together form a massive outerlayer of the thermoplastic material A, is preferably manufactured byextruding the thermoplastic material A into a pre-formed work piece,which extruded work piece is provided with a desired shape by vacuumforming and/or blow moulding. Alternatively the first and second layersre manufactured by the process of gas assisted injection moulding. Theintermediate expanded layer of the thermoplastic material B ismanufactured together with the extruding of the first and the secondouter layer of the thermoplastic material A which together form the workpiece, or by filling a hollow space between the first and the secondouter layer with the expanded thermoplastic material B by injectionmoulding. The functional parts are suitably integrated with the plasticarticle by injection moulding, press moulding, welding, confounding,gluing, riveting, screwing, snap-in joining or the like.

The article made of plastic material is suitably manufactured through aprocess including the steps;

a) forming of a solid outer layer,

b) manufacturing of an intermediate expanded layer and,

c) the appendage of functional parts such as reinforcing profiles,guiding profiles, stacking profiles, hinge parts, pockets, labelholders, profiles or holes for automatic handling, locking devices orthe like.

The solid outer layer is then manufactured by;

a, i) injecting an amount of molten thermoplastic material A into themould cavity of a mould, which molten thermoplastic material is allowedto solidify somewhat closest to the walls of the mould cavity. Apressurised gas is hereafter injected into the molten thermoplasticmaterial so that a gas cavity surrounded by thermoplastic material isformed in the mould cavity. The thermoplastic material is allowed tosolidify further after which the gas in the cavity is ventilated and atwin-walled, hollow article is obtained.

The solid outer layer is alternatively manufactured by;

a, ii) extruding a molten thermoplastic material A into a sheet or tubeshaped work piece. The work piece is applied in a mould for vacuumforming and/or blow moulding while still in a molten or semi-moltenstate. The mould cavity of the mould forms at least the main features ofthe article by forcing the work piece towards the shape-giving walls ofthe mould cavity by means of gas pressure and/or vacuum. The outer skinof a hollow, twin-walled article is hereby formed.

The intermediate expanded layer is manufactured by;

b, i) injecting a second amount of molten thermoplastic material B, towhich material an expanding agent has been added, into the hollow space.The thermoplastic materials A and B are allowed to solidify completely,whereby a laminate is formed. The laminate is composed of a first and asecond layer of solid thermoplastic material A and an intermediate layerof expanded thermoplastic material B with an average density of 50-800kg/m³.

The intermediate expanded layer is alternatively manufactured by;

b, ii) adding a further molten thermoplastic material A and a moltenthermoplastic material B, to which material B an expanding agent hasbeen added, to the so-called work piece which forms a first layer. Thefurther thermoplastic material A and the expanded material B are appliedto the first layer by extrusion, preferably together with the extrusionof the first layer. A laminate is hereby formed, which laminatecomprises a first and a second layer of a solid thermoplastic material Aand an intermediate layer of an expanded thermoplastic material B withan average density of 50-800 kg/m³. The layers, together, forms the tubeor sheet shaped work piece. The work piece is applied in the mould forvacuum forming and/or blow moulding, preferably while still in a moltenor semi-molten state. The mould cavity of the mould form at least themain features of the article by forcing the work piece towards theshape-giving walls of the mould cavity by means of low gas pressureand/or vacuum.

The functional part are integrated with the article by;

c, i) providing the mould cavity of the mould with pre-producedfunctional parts. The parts are preferably made of a material,compatible to, or the same as, the thermoplastic materials A and B. Thepre-produced functional parts are applied in pockets in the mouldcavity. The pockets are intended to receive the functional parts Thefunctional parts confound with, or are mechanically bonded to, the mainpart of the article consisting of the material of the work piece.

The functional part are alternatively integrated with the article by;

c, ii) providing the mould cavity of the mould with special cavitieswhich are negative depictions of the functional parts. The specialcavities are filled with a molten thermoplastic material C by means of ahot runner system arranged in the mould whereby the functional parts areformed. The functional parts confound with, or are mechanically bondedto, the main part of the article consisting of the material of the workpiece.

The functional part are alternatively integrated with the article by;

c, iii), providing the mould cavity of the mould with special cavitieswhich are negative depictions of the functional parts and movable mouldmembers placed on the opposite side of the mould cavity. The movablemould members force the still soft thermoplastic material into thespecial cavities in connection to the forming of the main features ofthe article. Functional parts integrated with the article are herebyformed.

The functional part are alternatively integrated with the article by;

c, iv) providing the article with pre-produced functional parts afterremoving the article from the mould. The functional parts are joinedwith the article by being screwed, riveted, glued, welded or snap-injoined.

The functional part are alternatively integrated with the article by;

c, v) providing the mould cavity of the mould, where the main featuresof the article is manufactured, with special cavities. The specialcavities are negative depictions of the functional parts. The moltenwork-piece is forced towards the surfaces of the mould cavity and intothe special cavities by means of high pressure and possibly vacuum sothat the skin of a hollow twin-walled article with integrated functionalparts is formed.

The functional part are alternatively integrated with the article by;

c, vi) providing the mould with special cavities which are negativedepictions of the functional parts so that pressurised injected moltenthermoplastic material is forced into the special cavities when injectedinto the mould cavity. The thermoplastic material is allowed to solidifysomewhat closest to the walls of the mould cavity before a pressurisedgas is injected into the mould so that a hollow space, surrounded bythermoplastic material, is formed in the mould cavity. The hollow spaceis hereafter filled with expanded thermoplastic material.

According to one embodiment of the invention the article is suitablymanufactured by a process including the three steps;

Manufacturing of a first and a second layer which together form a solidskin of an thermoplastic material A.

Integration of functional parts.

Manufacturing of an intermediate layer made from an expandedthermoplastic material B.

The process is initiated by injecting an amount of molten thermoplasticmaterial A into the mould cavity of a mould. The thermoplastic materialis allowed to solidify somewhat closest to the surface of the mouldcavity after which a pressurised gas is injected into the moltenmaterial. A gas cavity surrounded by thermoplastic material is herebyformed in the mould cavity. The thermoplastic material is allowed tosolidify further, after which the gas is ventilated from the cavity anda hollow, twin-walled article is formed.

The mould cavity, where at least the main features of the article ismanufactured can suitably be provided with special cavities. Thesespecial cavities are negative depictions of functional parts. The moltenthermoplastic material, which is injected into the mould cavity underpressure, is allowed to enter said special cavities as well. Functionalparts which are integrated with article are hereby formed. It is, ofcourse possible to integrate pre-produced functional parts with thearticle after the moulding procedure by gluing, screwing or welding themon to the article. It is, however, advantageous if the functional partscan be integrated with the article in the mould since the manufacturingtolerances will be better as well as an extra working operation will becancelled.

The intermediate expanded layer i manufactured by injecting a secondamount of thermoplastic material B into the hollow space. An expandingagent is added to the material prior to the injection. The thermoplasticmaterials A and B are then allowed to solidify completely. A laminate ishereby manufactured, which laminate is composed of a first and a secondlayer of a solid thermoplastic material A and an intermediate layer ofan expanded thermoplastic material B with an average density of 50-800kg/m³. The filling with expanded material is advantageously made whilethe article is still in the mould.

According to an alternative procedure, an article according to theinvention is manufactured according to a process including the threesteps;

Manufacturing of a first and a second layer which together form a solidskin of a thermoplastic material A.

Manufacturing of an intermediate layer made from an expandedthermoplastic material B

Integration of functional parts.

The process is initiated by extruding a molten thermoplastic material Ainto a tube or sheet shaped work piece. The work piece is then appliedin a mould for vacuum forming and/or blow moulding, preferably while thematerial in the work piece is still in a molten or semi-molten state.The mould provides the main features of the article by forcing the workpiece towards the shape-giving surfaces of the mould by means of gaspressure and/or vacuum. The skin of a twin-walled hollow article ishereby formed.

Functional parts can, to a certain extent, be made already here byproviding the mould with special cavities which are negative depictionsof functional parts in addition to the main features. The molten workpiece is under influence of a high gas pressure and possibly a vacuumforced towards the shape-giving surfaces of the mould and into thespecial cavities. The mould can alternatively be provided withpre-produced functional parts prior to the initiation of the mouldingprocedure. These functional parts are preferably manufactured from amaterial compatible with, or the same as, the thermoplastic materials Aand B. The pre-produced functional parts are applied in special pocketsin the mould cavity whereby they will confound with, or are mechanicallybonded to, the material of the work piece, in connection to the formingof the main features of the article.

According to yet another alternative, the mould is provided with specialcavities which are negative depictions of the functional parts andmovable mould members placed on the opposite side of the mould cavity.The movable mould members locally force the still soft thermoplasticmaterial into the special cavities in connection to the forming of themain features of the article. Functional parts integrated with thearticle are hereby formed. It is, of course possible to integratepre-produced functional parts with the article after the mouldingprocedure by gluing, screwing or welding them on to the article. It is,however, advantageous if the functional parts can be integrated with thearticle in the mould since the manufacturing tolerances will be betteras well as an extra working operation will be cancelled.

The intermediate expanded layer i manufactured by injecting a secondamount of thermoplastic material B into the hollow space. An expandingagent is added to the material prior to the injection. The thermoplasticmaterials A and B are then allowed to solidify completely. A laminate ishereby manufactured, which laminate is composed of a first and a secondlayer of a solid thermoplastic material A and an intermediate layer ofan expanded thermoplastic material B with an average density of 50-800kg/m³. The filling with expanded material is advantageously made whilethe article is still in the mould.

According to yet another procedure, an article according to the presentinvention is manufactured through a process including the three steps;

Manufacturing of a first and a second layer which together form a solidskin of a thermoplastic material A.

Manufacturing of an intermediate layer made from an expandedthermoplastic material B

Integration of functional parts.

The alternative procedure is initiated by melting the thermoplasticmaterials A and B. An expanding agent has been added to the material B.The two materials are extruded into a tube or sheet shaped work piece sothat the thermoplastic material B is on both sides surrounded by thethermoplastic material A. The work piece is then applied in a mould forvacuum forming and/or blow moulding, preferably while the material inthe work piece is still in molten or semi-molten state. At least themain features of the article is manufactured in the mould by forcing thework piece towards the shape-giving surfaces of the mould by means of alow gas pressure and/or vacuum. The skin of a twin-walled hollow productis hereby obtained. The thermoplastic material B is provided with anexpanding agent so that the average density of the intermediate layerlies within the range 50-800 kg/m³.

Foundations for functional parts are then manufactured by locallypressing the still soft thermoplastic material together. Theintermediate layer will hereby be compressed or densified so that thefirst and the second layer together with the intermediate layer form oneor more local, solid parts. The densified parts correspond with theparts where the functional parts are to be applied or, constitutefunctional parts per se. The article can also be provided withfunctional parts by providing the mould with special cavities which arenegative depictions of the functional parts. The special cavities arefilled with a molten thermoplastic material C via a hot runner system inthe mould. Functional parts will hereby take form in the mould, whichfunctional parts will confound with the rest of the article. Thethermoplastic material C is suitably injected with a low pressure, tocounteract an unintended collapse of the intermediate expanded layer.This can be achieved by injecting the thermoplastic material C through abranched hot runner which is provided with a number of valves inconnection to the mould cavity. The valves are opened as the specialcavities are filled so that the cavities are sequentially filled. Thethermoplastic materials A, B and C are compatible with each other,preferably the same thermoplastic material. The mould cavity of themould can also be provided with special cavities which are negativedepictions of the functional parts and movable mould members placed onthe opposite side in the mould. The movable mould members will locallyforce the still soft thermoplastic material into the special cavities inconnection to the manufacturing of the main features of the article.Functional parts integrated with the article will hereby be obtained.

The mould cavity of the mould can alternatively be provided withpre-produced functional parts prior to the initiation of the-mouldingprocedure. These functional parts are preferably made from the same, ora material compatible to the thermoplastic materials A and B. Thepre-produced functional parts are applied in pockets, intended toreceive the functional parts, in the mould cavity. The functional partswill hereby confound with, or be mechanically bonded to the material inthe work piece in connection to the manufacturing of main features ofthe article. It is, of course possible to integrate pre-producedfunctional parts with the article after the moulding procedure bygluing, screwing or welding them on to the article. It is, however,advantageous if the functional parts can be integrated with the articlein the mould since the manufacturing tolerances will be better as wellas an extra working operation will be cancelled.

According to one embodiment of the invention, foundations for functionalparts are manufactured by locally pressing the still soft thermoplasticmaterial together. The intermediate layer will hereby be compressed ordensified so that the first and the second layer together with theintermediate layer form one or more local, solid parts. The densifiedparts corresponds with the parts where the functional parts are to beapplied or, constitute functional parts per se.

Functional parts can suitably be manufactured by injecting a moltenthermoplastic material C under a low pressure. This is suitably achievedby injecting the thermoplastic material C through a branched type of ahot runner system, provided with a number of valves in connection to themould cavity. The valves are opened as the special cavities are filledso that the cavities are sequentially filled.

The thermoplastic materials A, B and C are compatible with each other,preferably constitute the same thermoplastic material. The thermoplasticmaterials A and C can for example be constituted by a high-densitypolyethylene while the thermoplastic material B is constituted by alow-density polyethylene or a re-cycled polyethylene.

What is claimed is:
 1. A process for the manufacturing of a hollowarticle made of plastic comprising a solid outer layer with anintermediate expanded layer and a functional part selected from thegroup consisting of reinforcing profiles, guiding profiles, stackingprofiles, hinge parts, pockets, label holders and profiles for automatichandling and locking, the process comprising: extruding a firstthermoplastic material into a sheet or tube shaped work piece forming afirst layer; adding further molten first thermoplastic material, moltensecond thermoplastic material and an expanding agent to the work pieceby extrusion to form a laminate comprising a first and a second layer ofsolid first thermoplastic material and an intermediate layer of anexpanded second thermoplastic material with an average density of 50-800kg/m³ which together forms the tube or sheet shaped workpiece; shapingthe workpiece by at least one method selected from the group consistingof vacuum forming and blow molding in a mold having a mold cavity withspecial cavities which cavities are negative depictions of thefunctional part, by means of at least one selected from the groupconsisting of gas pressure and vacuum; filling the special cavities witha molten third thermoplastic material to form the functional part; andintegrating the functional part with the remainder of the article.
 2. Aprocess according to claim 1, further comprising: pressing the laminatetogether locally while the thermoplastic materials are still soft sothat the intermediate layer is compressed or densified, and forming oneor more solid sections conforming with sections to which the functionalpart is to be applied.
 3. A process according to claim 1, comprisinginjecting the third thermoplastic material under low pressure to formthe functional part.
 4. A process according to claim 3, comprisinginjecting the third thermoplastic material through a branched hot runnersystem which is provided with a number of valves in connection to themold cavity, which valves are sequentially opened as a plurality offunctional parts are filled with molten third thermoplastic material sothat the functional parts are sequentially filled to form the functionalparts.
 5. A process according to claim 1, wherein the first, second andthird thermoplastic materials are of compatible thermoplastic materials.6. A process according to claim 5, wherein the first, second and thirdthermoplastic materials are the same thermoplastic material.
 7. Aprocess according to claim 1, wherein the first layer is co-extruded inthe adding step.
 8. A process according to claim 1, wherein the firstthermoplastic material, second plastic material and third thermoplasticmaterial are independently selected from the group consisting ofpolyethylene, polypropylene, polybutene, polyvinylchloride,polyalkylene-terephthalate, polystyrene, andacrylonitrile-butadiene-styrene co-polymer.
 9. A process according toclaim 1, wherein said integrating comprises at least one of injectionmolding, press molding, welding, confounding, screwing, riveting,gluing, and snap-in joining.
 10. A process according to claim 1, whereinthe first thermoplastic material comprises high-density polyethylene,the second thermoplastic material comprises a material selected from thegroup consisting of low-density polyethylene and re-cycled polyethyleneand the third thermoplastic material comprises high-densitypolyethylene.
 11. A process according to claim 1, wherein theintegration is performed while the article is in the mold.
 12. A processaccording to claim 1, wherein the filling is performed while the articleis in the mold.
 13. A process for the manufacturing of a hollow articlemade of plastic comprising a solid outer layer with an intermediateexpanded layer and a functional part selected from the group consistingof reinforcing profiles, guiding profiles, stacking profiles, hingeparts, pockets, label holders and profiles for automatic handling andlocking, the process comprising: extruding a first thermoplasticmaterial into a sheet or tube shaped work piece forming a first layer;adding further molten first thermoplastic material, molten secondthermoplastic material and an expanding agent to the work piece byextrusion to form a laminate comprising a first and a second layer ofsolid first thermoplastic material and an intermediate layer of anexpanded second thermoplastic material with an average density of 50-800kg/m³ which together forms the tube or sheet shaped workpiece; shapingthe workpiece by at least one method selected from the group consistingof vacuum forming and blow molding in a mold having a mold cavity bymeans of at least one selected from the group consisting of gas pressureand vacuum; providing the mould cavity with pre-produced functionalparts, wherein the functional parts are applied in pockets in the mouldcavity; and integrating the functional parts with the remainder of thearticle.
 14. A process according to claim 13, wherein the providingcomprises filling the mould cavity with a third thermoplastic material.15. A process according to claim 14, wherein the first, second and thirdthermoplastic materials are of compatible thermoplastic materials.
 16. Aprocess according to claim 15, comprising injecting the thirdthermoplastic material through a branched hot runner system which isprovided with a number of valves in connection to the mold cavity, whichvalves are sequentially opened as a plurality of functional parts arefilled with molten third thermoplastic material so that the plurality offunctional parts are sequentially filled to form the functional parts.17. A process according to claim 14, wherein the first, second and thirdthermoplastic materials, are the same thermoplastic material.
 18. Aprocess according to claim 14, wherein the first thermoplastic material,second plastic material and third thermoplastic material areindependently selected from the group consisting of polyethylene,polypropylene, polybutene, polyvinylchloride,polyalkylene-terephthalate, polystyrene, andacrylonitrile-butadiene-styrene co-polymer.
 19. A process according toclaim 13, wherein the first thermoplastic material compriseshigh-density polyethylene, the second thermoplastic material comprises amaterial selected from the group consisting of low-density polyethyleneand re-cycled polyethylene and the third thermoplastic materialcomprises high-density polyethylene.
 20. A process according to claim13, further comprising: pressing the laminate together locally while thethermoplastic materials are still soft so that the intermediate layer iscompressed or densified, and forming one or more solid sectionsconforming with sections to form the functional parts.
 21. A processaccording to claim 13, wherein the first layer is co-extruded in theadding step.
 22. A process according to claim 13, wherein saidintegrating comprises at least one of injection molding, press molding,welding, confounding, screwing, riveting, gluing, and snap-in joining.23. A process according to claim 13, wherein the integration isperformed while the article and the functional part are in the mold.